1. Field of the Invention
The present invention relates to an optical recording medium which can optically write and read information.
2. Related Background Art
Optical recording media conventionally demanded are those wherein a change of shape, change of structure or change of a constant of a physical property, is caused in a medium to thereby write and read information.
Known products that can satisfy such a demand may include, for example, those wherein pits are made in a recording layer with use of a dye or pigment as disclosed in Japanese Patent Laid-Open No. 82645/1984; those wherein pits are made in a metallic film as disclosed in Japanese Patent Laid-Open No. 96716/1974; those wherein a metallic film is transformed as disclosed in Japanese Patent Laid-Open No. 171689/1984; those wherein a change of an optical constant due to a change from the crystal phase to the amorphous phase is utilized as disclosed in Japanese Patent Laid-Open No. 46317/1975; etc.
On the other hand, there is known an optical recording medium of the type wherein the change of shape is caused in a recording layer.
As materials that can cause such a change of shape in a recording layer, low melting metals such as Te, Bi, Sn, Sb and In, or dyes or pigments (organic colorants) of cyanine type, squarium type, phthalocyanine type or methine type are known to have been used in some examples. However, in the case of the metals, containing less absorptive components, a high power is required for the "writing", and, in the case of the organic colorants, the reflectance thereof is so low that the S/N ratio can not be higher, obtaining no satisfactory results in either of the cases.
For this reason, an optical recording medium comprising a recording layer formed by laminating a reflective layer formed by the metals and an absorptive layer formed by the organic colorants has been proposed in Japanese Patent Laid-Open No. 45642/1984, etc.
On the other hand, in the above optical recording medium, it is required to previously provide pre-grooves (or guide grooves) for assisting a tracking servo, or address data for controlling the recording of data, in order to increase the capacity and enhance the reliability in writing and reading information.
For this purpose, as usually called "pre-formatting" and generally used in an optical disc or the like, a substrate 1 is grooved with a given style as shown in FIG. 3 and an optical recording layer 2 formed by laminating a light-absorptive layer 3 and a light-reflective layer 4 is provided on the substrate, thus performing the pre-formatting.
As a method therefor, there is the so-called 2P method in which an ultraviolet-curable type resin is applied on a substrate and the information having been pre-formatted is transferred to its surface by means of a stamper, or a method in which the transfer is carried out by forming a stamper in a mold at the time of the injection molding of a substrate.
However, when the optical recording portion is comprised of a light-reflective layer and a light-absorptive layer as shown in FIG. 3, there is a problem that the pre-format formed on the substrate can not be reproduced with good precision.
In other words, the tracking can be achieved only with difficulty at the time of the writing and reading, and also performance errors may be increased. As a result, the reliability on the information to be written and read may be lowered.